Peripheral artery disease (PAD) is a prevalent atherosclerotic disorder characterized by plaque build-up in the lower extremities. Functional limitations resulting from PAD lead to poor quality of life, high health care utilization and costsof care, and an increase in mortality risk. Current estimates suggest that PAD affects 6.3% of Americans, including 20% of individuals age 65 years and older. A diagnosis of PAD suggests presence of atherosclerosis in other vascular beds, and PAD significantly increases the risk of coronary and cerebrovascular disease events. The direct and indirect contribution of this disease to the morbidity associated with other chronic disease conditions is important yet health professional and public awareness of PAD is low in comparison with awareness of other chronic cardiovascular diseases; up to 50% of those with PAD are unaware they have the disease and physicians often do not evaluate for the presence of PAD. Disease awareness is critical as the burden of PAD is expected to increase as our population ages. Most PAD reports likely underestimate PAD burden as published findings are largely based on hospitalized events, to the exclusion of the prevalent outpatient PAD clinical encounters. Information concerning the temporal patterns associated with PAD-related clinical care is likewise limited by the lack of research that would take into account events occurring in both the inpatient and outpatient settings. Thus, PAD is an understudied disease of public health significance. The aims of this proposed study are: to estimate the burden of clinically diagnosed PAD and its major subtypes and to estimate the temporal patterns associated with PAD-related clinical encounters from 2003-2012 using Center for Medicare and Medicaid Services (CMS) claims data available for all residents of four geographically defined US regions comprising the Atherosclerosis Risk in Communities (ARIC) Study, a large observational study of the etiology of atherosclerotic diseases. These claims will allow examination of PAD in the context of communities for which a wealth of information concerning comorbid conditions and other cardiovascular diseases exists. In the proposed research we will also take advantage of data from the ARIC Study cohort, which have been linked with CMS Medicare claims. We will use these two data sources to estimate the predictive value (i.e. calibration factors) of CMS Medicare claims in the identification of PAD We will use these calibration factors to calculate adjusted prevalence and incidence of PAD. Administrative claims provide extensive information on clinical encounters occurring in multiple clinical settings and, as such, constitute a rich resource for the examination of the epidemiology of PAD. Results of the proposed research will create a foundation for future studies aimed at comparing, by demographics and comorbid conditions, the different trajectories associated with clinically manifest PAD diagnosed in the inpatient or outpatient setting.